Studies in this Section have led to a hypothesis that the amino acid sequences of native proteins carry information for specific global cooperative interactions operational only in uniquely folded structures to stabilize the structures. These unique structures would be the native structures. Some 22% of the amino acid residues of eucaryotic cytochrome c are invariant. We have speculated that requirement of global cooperative interactions for their operation might have imposed invariance to some of these residues. In testing this idea using a three-fragment complex of cytochrome c, we have found that replacement of invariant leucine 32 even with isoleucine or norvaline has profound effect in destabilizing the structure while replacement of variant leucine 35 with isoleucine has no effect. Both residues 32 and 35 are buried within the structure of native cytochrome c. Thus, studies of the effect of replacement of invariant residues on molecular motion might give an insight into the mechanism of global cooperative interactions. On the basis of this idea several lines of investigation with cytochrome c are in progress as follows. 1) Invariant Leu 32 and variant Leu 35: nine analogs of fragment (28-38) containing a substitute at one of these two residues have been synthesized to test for the effect on the global cooperative interactions. 2) Invariant Pro 30 and Gly 34: Three 3H-labelled analogs of (28-38) containing a substitute at one of these positions have been synthesized to test for the effect on binding with complex (1-25)H.(39-104) and the effect on the global cooperative interactions. 4) NMR studies: concerted motions of protein molecules would be controlled by global cooperative interactions. Thus, 1H NMR studies, including two-dimensional NMR, of the fragments complexes of cytochrome c have begun to determine such concerted motions. The studies will be extended to 13C NMR. Information will be collected and interpreted as a function of replacement of amino acid residues and change in the valence state of heme iron under different temperature conditions. The aim of this project is to obtain a key in predicting the three-dimensional structure to give the function on the basis of the amino acid sequence.